This specification relates to representing ranges of image data at multiple resolutions, for example, in the form of a histogram or other suitable graphical representation.
A graphical user interface (GUI) of an image processing application can display digital images along with one or more indicators to present information associated with the displayed image. In addition, the GUI can present controls that enable a user of the image processing application to adjust the displayed image based on the information shown by the indicators. FIG. 1A shows an instance of such GUI 100 that displays a view of an image 105. A histogram of the luminance 130 of the image 105 is represented in an indicator 120 of the GUI 100. Bins on the horizontal axis of the histogram indicator 120 represent luminance levels (values) of pixels in the image 105. The scale of the horizontal axis of the luminance histogram 130 has a single resolution over the entire range from 0.0 to 1.0, with bin “0.0” (the first or left-most bin) corresponding to black, and with bin “1.0” (the last or right-most bin) corresponding to white. The right-most bin is the 255th bin for an 8-bit image, or the 65,535th bin for a 16-bit image. In this example, the image 105 is an image in the RAW format (henceforth a RAW image) which contains extended range data corresponding to luminance levels in the range 1.0-2.0, in addition to image data corresponding to luminance levels in the range of 0.0-1.0. Pixels forming the image 105 that have luminance levels equal to and larger than 1.0 are represented (counted) by the histogram indicator 120 as part of bin “1.0”. Thus, for this image 105, the histogram indicator 120 displays a large histogram peak 132 for the luminance level=1.0.
In addition, a control 110 of the GUI 100 is used to adjust exposure of the image 105 by setting the position of a slider 115. The value of the exposure slider 115 depicted in FIG. 1A corresponds to the unadjusted image 105. Adjustment of the image exposure can be performed by the user of the image processing application using slider 115 and based on visual feedback conveyed by the luminance histogram 130. Results of an exposure adjustment are shown in FIG. 1B, where another instance of the GUI 100 displays a view of the adjusted image 105′. In this case, the user set another position of the slider 115′ associated with the exposure adjustment control 110. FIG. 1B shows that additional detail has been recovered and is now visible in the highlights of the adjusted image 105′ as a result of this exposure adjustment. The indicator 120 now shows a luminance histogram 135 of the adjusted image 105′. The luminance levels of the adjusted image 105′ are rescaled (compressed) by a factor proportional to the position of the slider 115′, in accordance with the overall darkening of the image. A portion 132′ of the luminance histogram 135 associated with the adjusted image 105′ corresponds to the peak 132 of the luminance histogram 130 associated with the image 105 prior to the exposure adjustment. The fact that the luminance histogram 135 associated with the adjusted image 105′ is distributed over most of the histogram portion 132′, as shown in the indicator 120, correlates to the noted additional detail that was recovered in the highlights of the adjusted image 105′.